Pneumatic striking tools have existed for several decades and may be constituted by, for example, drilling machines with striking impact or breakers. The striking tools may be hand-held by an operator or arranged on a rig and may be used vertically or horizontally. Regardless of the application range, all the striking tools have in common that they comprise a striking mechanism with a striking piston arranged in a striking mechanism housing. The striking piston is arranged for reciprocating motion by impact of supplied compressed air. The striking piston is moved forward by compressed air and strikes an insert tool, such as a drilling steel, an iron bar or similar at its front position, and an impact wave transmission to the insert tool is thereby achieved. After the strike against the insert tool, compressed air is supplied such that the striking piston obtains a return movement.
The pressure build up that occurs in the striking mechanism to accelerate and move the striking piston generates reaction forces. These reaction forces affect the striking mechanism housing and cause vibrations which may be perceived as unpleasant for the operator. Today, there are restrictions on how much vibration an operator should be exposed to daily. Machines with high vibration levels may thus be used for a shorter time than machines with low vibration levels. It is desirable to minimize the arising vibrations from the striking tool and thus prolong the time that an operator can work with the striking tool without negative impact. The vibrations of the striking mechanism housing, the insert tool and venting of the compressed air also cause unwanted sound emissions, which may be perceived as disturbing for people in the surrounding area. Furthermore, the vibrations result in fatigue loads of the striking tool.
Various solutions to minimize the occurrence of vibrations and noise emissions exist on the market. According to one solution, the handle of the striking tool is spring suspended, which reduces the vibrations of the striking tool. According to another solution, a sound dampening casing is arranged around the striking mechanism housing to reduce sound emissions.
Document SE383281 shows a striking tool comprising a striking piston movably arranged in a cylinder, which has a front and a rear cylinder chamber. To reduce the reaction forces arising at the striking tool and the thereby arising vibrations, compressed air is supplied with a substantially constant pressure to the rear cylinder space, which both accelerates the striking piston forward and decelerates the striking piston at its backward movement. Cavities arranged at the striking piston causes compressed air to be supplied to the front cylinder space and an accumulator, which results in that the striking piston is moved backward in the cylinder. Due to the limited size of the accumulator chamber a pressure is however built up in the front cylinder chamber upon striking, which decelerates the striking piston and reduces the striking tools striking impact. The configuration of the striking tool also results in throttling of the compressed air supply and thereby pressure drop when the striking piston shall be accelerated. The pressure drop generates heat, which causes a reduced efficiency of the striking tool.
Despite known solutions in the field, there is a need to achieve an ergonomical striking tool with minimal vibrations and sound emissions while generating required striking force.